This invention relates to the removal, from the cooling and lubricating fluid used for precision machining of metal objects, of the particles entrained in the fluid during machining. Such machining includes the boring of accurate holes in large metal objects (as, for example, the boring of cannon) and the formation of metal objects by grinding.
These entrained particles are of two kinds: (1) "swarf", that is, chips, shavings, and other fine particles removed from the work piece by the grinding or boring tools, and (2) "fines", whose definition is either (a) "particles smaller than average in a mixture of particles varying in size" or "fine material which passes through a standard screen on which coarser fragments are retained".
In the early 1940s Watervliet Arsenal installed a huge settling tank, measuring 10 ft..times.10 ft..times.10 ft., that held about twenty drums of oil. This tank supplied clean, cool oil for cannon honing. The tank required cleaning once a year to remove entrained particles. It had be pulled out of the ground to be hand cleaned with shovels, because swarf mixed with fines becomes a hard, caked material when both are allowed to settle together in a settling tank. The cleaning was very costly, requiring between forty and eighty hours of manual labor, during which time no boring or grinding could be carried out.
Cooling systems of smaller size replaced this large tank in the newer machinery installed in American arsenals. The smaller cooling systems relied on filters to remove swarf and fines. These filters require regular cleaning at weekly intervals, which also results in large amount of downtime. Four to twelve man-hours of cleaning labor per week is necessary. Also, these filters do not remove all the fines. These fines get deposited all over the machine and operating area, which leads to substantial equipment damage because of wear.
The best system presently available for removing entrained particles incorporates a magnetic filter. A series of magnets catches most of the metal swarf. The swarf forms a porous filter medium that screens out most of the stone particles, those that are twenty microns and larger. The rest of the particles, especially the fines, remain in the fluid. They are agitated so that they do not settle, and they are then removed by a costly system that uses a pleated cartridge filter.